Electrical service providers such as electrical utilities employ electricity meters to monitor energy consumption by customers and other entities. Electricity meters track the amount of energy consumed by a load (e.g. the customer), typically measured in kilowatt-hours (“kwh”), at each customer's facility. The service provider uses the consumption information primarily for billing, but also for resource allocation planning and other purposes.
Many current electricity meters employ digital circuitry to determine energy consumption and other billing values. For example, it is known to use digital signal processors to calculate energy consumption from digital energy measurement signals. The calculated consumption information is then displayed on a meter display. From time to time, a meter reader from the utility obtains the consumption information displayed on the customer's meter display to facilitate billing. In the alternative, or in addition, the meter may include transmission capabilities for transmitting consumption information to a remote utility computing device, thereby also facilitating billing.
Electrical power is transmitted and delivered to load in many forms. For example, electrical power may be delivered as polyphase wye-connected or delta-connected power or as single phase power. Such various forms are known as service types. Different standard electricity meter types, known as meter forms, are used to measure the power consumption for the various service types. The commonly used meter forms in the United States include those designated as 2S, 3S, 5S, 45S, 6S, 36S, 9S, 16S, 12S and 25S meter forms, which are well known in the art.
As discussed above, a primary purpose of metering is to determine energy usage by a load (customer) for the purposes of accurate billing. It is therefore known that tampering with an electricity meter can result in reduced billing costs, and stolen energy. Typical tampering techniques involve either disabling the meter itself, or bypassing the meter completely. Many types of tampering involve removal of the meter cover or removal of the meter itself. Removal of the meter cover, for example, can allow for disabling or adjustment of the meter circuitry. In some cases, the circuitry may be disabled and/or adjusted and the meter cover replaced in order to mask the tamper event.
To combat energy theft via tampering, it is known to provide mechanical switch mechanisms that are triggered by cover removal, meter removal, impact, and other common operations related to tampering. Such mechanical switches generate outputs that are detected by the meter processing circuitry, which may then record the event for display or transmission to the utility.
Nevertheless, one remaining issue with tamper detection relates to power outages. In particular, electricity meters that have processing circuitry typically obtain operating power from the power lines connected to the meter. Accordingly, when a power outage occurs, primary power to the meter circuits is lost. Many meters employ temporary back-up power to allow for a graceful power down, and in some cases to allow some low level processing. Nevertheless, it is typical for one or more processing devices to be placed in “sleep” mode, which is a highly reduced state in which only a clock is maintained, and one or two inputs monitored.
In general, lack of processing during a power outage is not detrimental to the primary purpose of the meter. To this end, no energy is delivered to the customer load during a power outage, and therefore the meter need not perform normal metering operations involving the processing circuits. However, the lack of processing operations can result in inability to detect certain tampering operations. For example, if the meter cover is removed during a power outage, and replaced before power is restored, then a tamper event could go undetected because the dormant processing circuit cannot monitor the inputs associated with tamper detection switches in the meter. Accordingly, there is a need for a method of detecting tamper events during a power outage.